The preparation of star-branched polymers comprising a nucleus joining polymeric arms of non-hydrogenated and hydrogenated homopolymers or copolymers of conjugated dienes or selectively hydrogenated copolymers of conjugated dienes and mono-alkenyl arenes is known. The nucleus of these polymers comprises a poly (polyvinyl aromatic) coupling agent such as poly(divinylbenzene) and can have 4 to 30 polymeric arms. The polymeric arms are polybutadiene or polyisoprene arms.
Multifunctional anionic initiators (Eschwey et al., Makromal. Chem. 173 (1973) 235 and Burchard et al., Polymer 16 (1975) 180) have been used as well as controlled amounts of bis-unsaturated monomers, usually divinyl benzene (Worsfold et al., Can. J. Chem., 47 (1969) 3379, Young et al., Macromolecules, 11 (1978) 899, Martin et al., Anionic Polymerization: ACS Symp. Ser., 166 (1981) 557). Most of the work in the area of star-branched polymers has been conducted using polystyrenes or polydienes. Relatively little work has been done with polymethacrylate star-branched polymers. Rather polydisperse materials which increased in viscosity and molecular weight on storage were prepared using group transfer polymerization (Simms et al., Rubber Chem. Technol. 64 (1991) 139). Zhu et al., Macromolecules, 25 (1992) 7330, Tsitsilianis et al., Macromolecules, 24 (1991), 5897 and Zilliox et al., J. Polym. Sci., Part C, 22 (1968) 148 have published reports in which star polymers from methacrylate were prepared.
There is, however, a present need for the preparation of star-branched polymers from acrylic or methacrylic monomers which have molecular weights and other physical characteristics which make them commercially useful in various applications including usefulness as lubricating oil additives.